Apparatus for bending plates with rolls

ABSTRACT

An apparatus for bending plates comprises a support structure ( 5 ) carrying two rollers ( 2, 3 ) and a pressure roller ( 4 ) which, in co-operation with each other, define a curved feeding path (P) for a plate (L) to be bent. The rollers ( 2, 3 ) are movable relative to the pressure roller ( 4 ) to vary at least one curvature value of the feeding path (P). The apparatus ( 1 ) further comprises a pair of articulated kinematic mechanisms ( 13 ) each of which acts on a respective roller ( 2, 3 ) to move said roller along a plurality of trajectories lying in a plane transverse to a rotation axis (X 1 , X 2 ) of the roller ( 2, 3 ).

The present invention relates to a calendering apparatus. In more detail, the apparatus in accordance with the invention applies to calendering of plates and more particularly to calendering of metal plates.

By the term calendering it is intended a mechanical working by plastic deformation carried out on plates of different materials to give the plates a pre-established bending. This working operation that can take place under heating or under cold conditions, consists in feeding a plate to a suitable bending machine, referred to as “calender”, which carries out bending of the plate itself around an axis.

The most widespread calenders among those presently on the market are provided with three rollers with parallel axes disposed in such a manner that the plate, for passage between them, follows a circular trajectory the radius of curvature of which can be adjusted by acting on the mutual position of the rollers. The rollers are carried by suitable supports or lateral walls of the calender, called sidewalls, that are shaped to securely receive members for guide, movement and support of the rollers. Usually, these guides are obtained in the sidewalls by milling operations defining sliding seats for the roller guide members.

In detail, in a three-roller calender of a first type; a first one of the three rollers is provided to rotate about a fixed axis, while the two other rollers can translate close to or away from the first roller to vary the radius of curvature of the path imposed to the plate. This takes place by providing suitable rectilinear guides in the sidewalls of the calender, within which the roller supports slide in such a manner that the rollers can be guided along pre-established trajectories. In particular, the guides present in each sidewall are rectilinear and tending to a point positioned in the vicinity of the first roller, to generate a mutual approaching of the movable rollers when the same are moved close to the first roller.

A second type of three-roller calender has sidewalls provided with rectilinear guides for translation of two rollers in the same direction, while a pressure roller can be moved close to the two other rollers in a direction perpendicular to said translation direction to determine a curved feeding path for the plate, in co-operation with said two rollers. In addition, following translation of the two rollers, a variation in the geometry of the path imposed to the plate takes place and in more detail, the more one of the two translatable rollers is close to the third roller, the more this path is curved.

A third type of calender that is presently known comprises a first pair of power driven transport rollers, rotating about fixed axes and through which the plate is forced to move forward. At laterally opposite positions relative to the power driven rollers there are located two other rollers that are translatable in a direction transverse to the feeding or advancing direction of the plate through the first pair of rollers. During feeding of the plate between the first pair of rollers, one of the two other rollers is moved along its translation direction for interfering with the normal feeding trajectory of the plate, forcing the latter to deform and take a permanent bending at a portion thereof facing the translated roller. Each of the two translatable rollers carries out generation of a bending in a corresponding portion of the plate.

The above described calenders have some important drawbacks.

The calenders of the first type do not succeed in carrying out bending of the end portions or headpieces of the plate concurrently with bending of the central portion of the plate itself, but bending of the headpieces must be carried out subsequently to bending of the central portion. In addition, the calenders of the first type do not tighten the plate between two rollers but they carry out dragging of the plate due to the frictional force generated between the plate and rollers following bending of the plate itself. Therefore, the force generated by friction greatly depends on the bending amount imposed to the plate.

When thin plates are being worked, the force transmitted by the rollers to the plate to deform it is relatively low, which will result in a low frictional force that will impair correct dragging of the plate during calendering.

In addition, expensive milling operations are required in the sidewalls for roller translation, in order to obtain the slide seats of the roller guide members.

The calenders of the second type as well have the drawback of requiring expensive working operations in the machine sidewalls so as to obtain, by milling, the long seats receiving the guide means for roller translation. These milling operations are much more demanding as compared with those in the calenders of the first type, due in particular to the travels carried out by the rollers during translation.

The calenders of the third type are much more expensive to manufacture, due in particular to the presence of four rollers instead of three. In fact the roller cost is the one that mostly weighs upon the machine manufacture.

In all types of calenders described above the rollers are translatable along pre-established directions, i.e. determined by the orientation of the milling operations defining the slide seats. As a result of this, it is to be added as a further drawback that the above calenders have a limited operating flexibility as they can be only used for a reduced number of operations allowed by the movements that the rollers can carry out.

Accordingly, it is a technical task of the present invention to make available a calendering apparatus that is devoid of the above mentioned drawbacks.

Within the scope of this technical task the present invention mainly aims at making available a calendering apparatus having a high degree of operating flexibility.

A further important aim of the invention is to provide a calendering apparatus capable of combining high performance with reduced manufacturing costs of the apparatus itself.

The foregoing and further aims that will become more apparent in the following of the present description are substantially achieved by a calendering apparatus having the features set out in claim 1 and/or in one or more of the claims depending thereon.

A preferred but not exclusive embodiment of a calendering apparatus in accordance with the present invention is now given by way of non-limiting example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view of a calendering apparatus in accordance with the invention, in a first operating configuration;

FIG. 2 shows a second operating configuration of the apparatus in FIG. 1;

FIG. 3 diagrammatically shows a detail of the apparatus in reference, sectioned along line in FIG. 1;

FIG. 4 shows a further detail of the apparatus in question, sectioned along line IV-IV in FIG. 2;

FIG. 5 is a side view of the apparatus in a third operating configuration.

In accordance with the accompanying drawings, an apparatus for putting into practice calendering processes for plates, preferably made of metal, is generally identified with reference numeral 1. This apparatus 1 is used in machines for calendering metal plates in which the plate is fed, by means of a roller bed for example, towards said apparatus 1 in order to be bent according to a final cylindrical or conical geometry.

Apparatus 1 comprises a first roller 2, a second roller 3 preferably identical with the first roller 2, and a pressure roller 4, co-operating with each other to define a curved feeding path “P” for a plate “L” to be bent.

Rollers 2, 3 and pressure roller 4 are preferably of cylindrical shape with a circular section having a slight convexity, and are rotatably disposed around respective rotation axes “X1”, “X2” and “X3” that, at least in the machining operations aiming at deforming plate “L” according to a cylindrical bending, are parallel to each other.

The rotation axis “X3” of pressure roller 4 is fixed, while the two rollers 2, 3 are movable close to and away from pressure roller 4 to vary the geometry of the feeding path “P” of plate “L”, and in more detail to vary a curvature value of such a path “P”.

Preferably, during their movement said rollers 2, 3 keep their rotation axes “X1”, “X2” parallel to the rotation axis “X3” of the pressure roller 4, to generate a cylindrical bending of plate “L”. In accordance with the view in FIG. 1, path “P” defined by the mutual position of rollers 2, 3 and pressure roller 4 is tangent to the two rollers 2, 3 and is substantially circular with a concavity facing upwards.

From the position shown in FIG. 1 an operating principle of apparatus 1 in accordance with the invention is inferred, in which plate “L” is retained between the first roller 2 and pressure roller 4, while the second roller 3 defines a rolling surface for plate “L” which is forced to bend under the dragging action along a feeding direction denoted at “A”. The rolling surface defined by the second roller 3 interferes with a tangent plane “T” that is common to the first roller 2 and the pressure roller 4, which tangent plane “T” represents a theoretical undeformed path, in particular substantially rectilinear, that would tend to maintain plate “L” in the absence of the intervention of the second roller 3.

In addition, the bending amount imposed to plate “L” is of such a nature as to generate a permanent set corresponding to a desired final deformation which is possibly accompanied by an elastic-deformation component that is taken up by spring-back of the material constituting plate “L” at the end of the calendering process.

Preferably, only pressure roller 4 is connected to respective power means not shown and adapted to move said pressure roller to generate feeding of plate “L” through apparatus 1. Advantageously, since plate “L” is forced to move forward under a mutual compression action exerted by the first roller 2 and pressure roller 4, no slippage of plate “L” relative to pressure roller 4 occurs and feeding of plate “L” takes place correctly.

Feeding of plate “L” is therefore advantageously independent of the thickness of said plate “L” and the bending value imposed to the latter.

According to a preferred embodiment of the invention, apparatus 1 comprises a support structure 5 performing a support and guide function for rollers 2, 3 and pressure roller 4. In detail, the support structure 5 comprises a pair of sidewalls 6 which are located at the opposite ends of rollers 2, 3 and pressure roller 4 to bear them at their ends.

As shown in FIG. 3, each sidewall 6 has a seat 7 into which a respective end of pressure roller 4 can be inserted through interposition of a first antifriction element, preferably a first adjustable bearing 8 and more preferably a barrel roller bearing. Said first antifriction element is fitted on a respective cylindrical end portion 9 of pressure roller 4, which has a radial size smaller than a corresponding radial size of a central portion 10 of the pressure roller 4 itself that is designed to come into contact with plate “L”.

Between said central portion 10 and cylindrical end portions 9, pressure roller 4 has connecting portions 14 of frustoconical shape.

Said first antifriction element is steadily housed in the respective seat 7, in accordance with said fixed positioning of the rotation axis “X3” of pressure roller 4.

Apparatus 1 further comprises guide means 12 for rollers 2, 3 which are connected to the support structure 5 and acts between rollers 2, 3 and the support structure 5 to move rollers 2, 3 close to and away from the pressure roller 4.

Advantageously, according to a preferred embodiment of the invention, the guide means 12 moves rollers 2, 3 along a plurality of trajectories lying in a plane transverse to the rotation axes “X1”, “X2” of rollers 2, 3 and, more preferably, perpendicular to the rotation axis “X3” of pressure roller 4. This allows an important operating flexibility to be achieved because rollers 2, 3 are movable in a plurality of directions belonging to said transverse plane, instead of being exclusively movable along a predetermined direction. This enables a plurality of operating configurations to be obtained that are different from each other and are suitably determined based on a pre-established calendering process to be put into practice and aimed at optimising a pre-established sequence in the calendering steps of a metal plate “L”.

In accordance with the accompanying figures, the guide means 12 comprises at least one articulated kinematic mechanism 13 having at least one support portion 14 for a respective one of rollers 2, 3 to move said roller 2, 3, during operation of the articulated kinematic mechanism, along a plurality of trajectories different from each other and belonging to said transverse plane.

According to a preferred embodiment of the invention, the guide means 12 comprises two articulated kinematic mechanisms 13 each of which has two support portions 14 for respective axial ends of the respective roller 2, 3. Only two of the four support portions 14 can be seen in FIGS. 1, 2 as the two other portions are aligned along the rotation axes “X1”, “X2” of rollers 2, 3; likewise, only two of the four support portions 14 can be seen in FIGS. 3, 4.

In more detail, each articulated kinematic mechanism 13 comprises at least one articulated quadrilateral 15 acting between the support structure 5 and the respective roller 2, 3. Preferably, each articulated kinematic mechanism 13 comprises two articulated quadrilaterals 15, each of which acts between the supporting structure 5 and an axial end “Z” of the respective roller 2, 3. The two articulated quadrilaterals 15 of each articulated kinematic mechanism 13 and more preferably all the four articulated quadrilaterals 15 are of identical construction and, consequently, only one of them and more particularly in relation to the first roller 2, will be hereinafter described for the sake of simplicity.

The articulated quadrilateral 15 comprises an arm 17 defining said support portion 14 of the first roller 2 and movable along a plurality of trajectories belonging to said transverse plane to make the first roller 2 take a plurality of operating positions relative to the pressure roller 4. It is therefore apparent that the first roller 2 is associated, at both its axial ends “Z”, to an arm 17 defining a corresponding support portion 14 of the first roller 2 itself.

Said support portion 14 carries out a rotational coupling between arm 17 and a cylindrical end portion of the first roller 2, preferably through interposition of a second adjustable bearing 19 and more preferably a bearing of the barrel roller type. Each cylindrical end portion 18 of the first roller 2 is connected to a central, preferably cylindrical, portion 20 of the first roller 2 through a frustoconical portion 21.

Arm 17 is rotatably in engagement, at a first portion 17 a thereof, with a fulcrum 22, and is further connected and operatively associated with a linear actuator 23 to be operated around said fulcrum 22. The linear actuator 23 is preferably a hydraulic cylinder or, more generally, a fluid-operated cylinder, and still more preferably a double-rod cylinder. Advantageously, fulcrum 22 is a movable fulcrum. Consequently, arm 17 is movable according to a rotation-translation movement obtained by the sum of a rotation movement around said fulcrum 22 and a translation movement of the fulcrum 22 itself.

In the preferred embodiment of the invention and as shown in the accompanying drawings, fulcrum 22 is movable along an adjustment path “R”, and in particular by means of a linear guide 24 having a major extension direction that is coincident with the adjustment direction “R”. The linear guide 24 comprises a screw threaded rod 24 a, aligned with said adjustment path “R”, and an internally threaded slider 24 b for coupling with the threaded rod 24 a by a lead nut-worm screw coupling. The threaded rod 24 a is borne and maintained in place by a pair of supports 24 c through third bearings 24 d that are preferably adjustable and more preferably of the barrel roller type, at least one of which has properties of axial constraint. Slider 24 b slides between the supports 24 c and in particular along a major extension direction of the threaded rod 24 a. In particular, slider 24 b receives a thrust action along the adjustment path “R” following a rotation of the threaded rod 24 a obtained by respective drive means “M”, preferably an electric motor. The particular conformation of the lead nut-worm screw coupling is also advantageous, due to the fact that a thrust on slider 24 b directed along the adjustment path “R” does not cause a corresponding rotation of the threaded rod 24 a, and therefore if the threaded rod 24 a is not driven, slider 24 b does not move and maintains a previously determined position in a stable manner.

The orientation taken instant by instant by arm 17 is therefore directly affected by the position of fulcrum 22, and therefore of slider 24 b, and by a configuration taken by the linear actuator 23. The latter, in particular, can take a plurality of positionings included between a rest condition at which it keeps the respective first roller 2 spaced apart from the pressure roller 4, a first operating condition, at which it keeps the first roller 2 in thrust relationship against the pressure roller 4 generating a grip action on plate “L”, and a second operating condition at which the first roller 2 interferes with the theoretical undeformed path of plate “L” to impart a bending to plate “L” moving it forward along said feeding path “P” when said plate is grasped between the second roller 3 and pressure roller 4.

These configurations are in any case affected by the position of fulcrum 22, a displacement of which gives rise to different configurations of the respective articulated quadrilateral 15 also with the same configurations of the linear actuator 23.

The linear actuator 23 is hinged at a first end thereof, to a second portion 17 b of arm 17 and is further advantageously hinged at a second end thereof to the support structure 5 of apparatus 1 by a fixed-axis hinge “C”.

Advantageously and in addition, the linear guide 24 is steadily connected to the support structure 5, by welding for example.

Concurrence of the just described connections makes apparatus 1 according to the invention of simple and cheap manufacture, since expensive machining operations are not required for the seats of sliding guides to be obtained by milling in the sidewalls 6. On the contrary, hinging of the linear actuator 23 and steady coupling of the linear guide 24 to the support structure 5 are connections of cheap construction and in addition the articulated kinematic mechanism 13 being of the isostatic type, creates an optimal redistribution of the efforts to which the different parts of the kinematic mechanism 13 itself are subjected. This isostatic character is given by the relative coupling between the linear guide 24, arm 17 and linear actuator 23 defining a triple-hinge arch when the position of slider 24 b along the adjustment path “R” has been fixed.

A further advantage is connected with the particular geometry of the above mentioned couplings. In detail, according to a view in FIG. 1, in the position at which the first roller 2 is pushed by arm 17 against the pressure roller 4, the linear actuator 23 associated with arm 17 is disposed along a plane passing through the rotation axis “X1” of the first roller 2 and the rotation axis “X3” of the pressure roller 4. This means that in the front view in FIG. 1, the linear actuator 23 in such a position is substantially aligned with the centres of the first roller 2 and the pressure roller 4. This alignment also comprises respective contact points between the first roller 2 and plate “L”, and between plate “L” and the pressure roller 4 that are aligned with said centres of the first roller 2 and pressure roller 4 to define an optimal condition for obtaining a correct bending action of the end portions, i.e. the ends, of plate “L”. Said contact points shown in the accompanying figures correspond to contact lines between plate “L” and rollers 2, 3 and/or pressure roller 4.

An optimal thrust geometry of the linear actuator 23 on the first roller 2 arises from said coplanarity between the linear actuator 23 and the rotation axes “X1”, “X3” of the first roller 2 and pressure roller 4, because the thrust action carried out by the linear actuator 23 is fully directed towards roller 2 and therefrom towards pressure roller 4, while no force is transmitted to fulcrum 22 or, in case of small misalignments, only a force of reduced amount is transmitted to fulcrum 22. This enables the sizes of the linear guides 24 to be reduced, as the latter are submitted to small stressed even under operating conditions.

Preferably, in addition, in the positions at which the first roller 2 is employed to generate bending of plate “L” as shown in FIG. 2, the linear actuator 23 generates a thrust towards the first roller 2 having a greater arm, with respect to fulcrum 22, than the arm of a corresponding opposite resisting force by plate “L”. During this step, the thrust action of the linear actuator 23 is directed along the linear actuator 23 itself since the latter is hinged at its ends, while the resisting action offered by plate “L” is oriented from the contact point between plate “L” and the first roller 2 towards the rotation axis “X1” of the first roller 2 itself. Therefore, the geometry of the hinging points disposed on arm 17 generates an advantageous lever effect reducing the thrust of the linear actuator 23, the thrust action necessary for bending plate “L” being the same.

The above is the same in a mirror image for the articulated kinematic mechanism 13 carrying the second roller 3. Apparatus 1 in fact can be indifferently used either if a plate “L” is fed from left to right in accordance with FIGS. 1 and 2, or if the same plate “L” is fed from right to left. This in addition allows different passages on the same plate “L” to be carried out, to gradually give the plate “L” different bending intensities, for example.

Hereinafter it will be summarised a principle of operation of apparatus 1 in accordance with the invention, for carrying out cylindrical calendering operations.

Starting from the position shown in FIG. 1, a plate “L” is fed to apparatus 1 along the feeding direction “A”, until a front end “L1” of plate “L” is brought close to the first roller 2 and pressure roller 4. In more detail, the front end “L1” of plate “L” is moved forward along the feeding direction “A” until it goes beyond the plane “Y1” passing through the rotation axis “X1” of the first roller 2 and the rotation axis “X3” of the pressure roller 4. This getting over preferably has an amount, just as an indication, corresponding to twice or three times the thickness of plate “L”, to ensure steady clamping of the latter between the first roller 2 and pressure roller 4.

Concurrently with this positioning of plate “L”, the second roller 3 is lifted until it intercepts plate “L” and lifts it generating bending of plate “L” at least at a portion thereof included between the two rollers 2, 3. Meanwhile, plate “L” is moved forward along the feeding direction “A” under a dragging action exerted by the pressure roller 4 connected with said respective drive means not shown. Advantageously, the clamping action exerted by the first roller 2 and pressure roller 4 promote moving forward of plate “L” while avoiding dangerous slippages between plate “L” and the first roller 2 and/or pressure roller 4.

To achieve a correct calendering of a rear end portion “L2” of plate “L”, rollers 2, 3 are moved to obtain a configuration that is substantially a mirror image of the configuration provided at the beginning. In detail, as shown in FIG. 2, the first roller 2 is moved away from pressure roller 4, and in particular it is located at a more forward position relative to pressure roller 4 along the feeding direction “A” of plate “L”, while the second roller 3 is brought to take the configuration initially taken by the first roller 2. In particular, the second roller 3 is moved close to pressure roller 4 to tighten plate “L” in co-operation with said pressure roller, in such a manner that the calendering operation can be continued.

While working is going on, the first roller causes bending of plate “L” while it is tightened between the second roller 3 and pressure roller 4, until a limit at which plate “L” has been submitted to the action of the pressure roller 4 over the whole length thereof, except a portion just as an indication equal to twice or three times the plate thickness, so as to maintain a correct clamping of plate “L” between the second roller 3 and pressure roller 4.

The front and rear end portions of plate “L” that are not bent at the end of the calendering operation, which on the other hand are of very reduced extension, can be removed or machined after mutual welding of the opposite ends “L1”, L2″ of plate “L”.

To carry out conical calendering, rollers 2, 3 are not pushed against the pressure roller 4 to tighten plate “L”, but they are moved close to the pressure roller 4 and inclined in such a manner that the respective rotation axes “X1”, “X2” form a non-zero angle relative to the rotation axis “X3” of the pressure roller 4.

In this configuration, pressure roller 4 is positioned between the two rollers 2, 3, as shown in FIG. 5. By suitably inclining the rotation axes “X1”, “X2” of the two rollers 2, 3, conical calendering operations according to different geometries can be generated.

In this configuration, due to lack of an aligned condition between the rotation axis “X3” of pressure roller 4, the rotation axis “X1”, “X2” of each of the two rollers 2, 3 and the respective contact points between pressure roller 4 and plate “L” and between plate “L” and each of the two rollers 2, 3, slippages of the plate against the surfaces of rollers 2, 3 and of pressure roller 4 are allowed, which slippages are necessary for conical calendering.

Advantageously, adopting the second bearings 19 of the type with adjustable rollers allows the inclination of the rotation axes “X1”, “X2” of the two rollers 2, 3 to be taken up, although within some limits structurally imposed by the bearings 19 themselves, without complicated articulation systems being required for taking up said inclinations.

Preferably, in addition, the first portion 17 a of each arm 17 and the respective slider 24 b are hinged on each other through a universal joint 25. This universal joint 25 enables relative rotation between the first portion 17 a of each arm 17 and the respective slider 24 b both around a first axis perpendicular to said transverse plane, already widely described in connection with fulcrum 22, and around a second axis belonging to said transverse plane. Rotation about said second axis allows the transverse plane to vary an inclination angle thereof relative to a vertical plane, therefore enabling the arm 17 to modify its inclination relative to the vertical plane, due to working defects or deformations under effort.

A control box, not shown, operates the linear actuators and linear guides 24 defining first and second actuator members of arms 17, respectively. Each linear actuator 23 and linear guide 24 is preferably controlled in an independent manner and is operated in association with the other linear actuators 23 and linear guides 24 to reach a pre-set operating configuration.

In detail, arms 17 associated with the two axial ends “Z” of each of the two rollers 2, 3 are operable in an independent manner, being regulated by the control box. This is advantageously useful in order to prepare apparatus 1 for conical calendering operations, in which the rotation axes “X1”, “X2” of rollers 2, 3 are inclined to the rotation axis “X3” of pressure roller 4 and therefore in which the arms 17 associated with each roller 2, 3 are at different heights from each other. This configuration is obtained by operating the two linear actuators 23 associated with each roller 2, 3 in a different manner.

Preferably, in addition, each arm 17 is associated with a respective linear guide 24 which determines a configuration of the respective arm 17 enabling, in co-operation with the opposite arm 17 of the same roller 2, 3, an inclination of the rotation axis “X1”, “X2” of the roller 2, 3 itself relative to pressure roller 4. As already shown, this inclination of roller 2, 3 does not interfere with a normal rotation of roller 2, 3 due to adoption of the second bearings 19 enabling inclinations of a width of some degrees to be taken up.

In the embodiment shown in FIGS. 1, 2, 5, the two articulated quadrilaterals 15 in sight are mutually disposed in such a manner that the corresponding linear actuators 23 face each other. This results in a symmetric and compact structure of apparatus 1. In other words, each linear actuator 23 associated with the first roller 2 is disposed in an intermediate position included between the respective linear guide 24 and second roller 3. According to said configuration of apparatus 1, the linear actuators 23 intended for movement of rollers 2, 3, are substantially located under said rollers 2, 3 to such a position that a thrust effect on rollers 2, 3 is maximised and transmission of mechanical actions onto the linear guides 24 is minimised.

In addition, it will be recognised that due to the possibility of adjusting the actuator members, i.e. the linear actuators and linear guides in an independent manner and due to the possibility of moving the rollers along a plurality of trajectories lying in said transverse plane, both cylindrical-calendering operations according to different curvatures and conical-calendering operations can be carried out with the same apparatus, so that a high operating flexibility will be achieved.

Advantageously and furthermore, these cylindrical and conical-calendering operations are carried out in an optimised manner and, in particular, due to the possibility of being able to machine the front and rear end portions of the plate simultaneously with bending of the central region of the plate itself, additional bending passages for the end portions of the plate are eliminated. 

1-16. (canceled)
 17. A calendering apparatus, comprising: a support structure (5), and at least two rollers (2, 3) and one pressure roller (4), said rollers (2, 3) and pressure roller (4) being carried by said support structure (5) and, in co-operation with each other, defining a curved feeding path (P) for a plate (L) to be bent, said rollers (2, 3) being in addition movable relative to the pressure roller (4) to vary at least one curvature value of said feeding path (P); guide means (12) connected to the support structure (5) and acting on said rollers (2, 3) to move the latter close to and away from the pressure roller (4); characterised in that said guide means (12) comprises, for at least one of said first and second rollers (2, 3), at least one articulated kinematic mechanism (13) having at least one support portion (14) for the respective roller (2, 3), said support portion (14) being movable along a plurality of trajectories lying in a plane transverse to a rotation axis (X1, X2) of the respective roller (2, 3), to move said roller (2, 3) in a plurality of directions relative to the pressure roller (4).
 18. An apparatus as claimed in claim 17, characterised in that said guide means (12) is movable according to a plurality of positions included between: a first operating position, at which said means arranges the rotation axis (X1) of the first roller (2), the rotation axis (X3) of the pressure roller (4), and respective contact lines between the plate (L) and said first roller (2) and pressure roller (4) in a mutually aligned position along a first common plane (Y1), while keeping the plate (L) pressed between the first roller (2) and pressure roller (4), and a second operating position at which said means arranges the rotation axis (X2) of the second roller (3), the rotation axis (X3) of the pressure roller (4), and respective contact lines between the plate (L) and said second roller (3) and pressure roller (4) in a mutually aligned position along a second common plane (Y2), while maintaining the plate (L) pressed between the second roller (3) and pressure roller (4).
 19. An apparatus as claimed in claim 17, characterised in that said support portion (14) can be rotatably moved around a movable fulcrum (22), rotation of the support portion (14) around said movable fulcrum (22) and displacement of the position of said fulcrum (22) allowing said support portion (14) to follow said plurality of trajectories.
 20. An apparatus as claimed in claim 17, characterised in that said at least one articulated kinematic mechanism (13) has at least one portion connected to the support structure (5) by a fixed-axis hinge (C).
 21. An apparatus as claimed in claim 20, characterised in that said fulcrum (22) is movable along a rectilinear adjustment path (R).
 22. An apparatus as claimed in claim 17, characterised in that said at least one articulated kinematic mechanism (13) comprises at least one arm (17) defining said support portion (14), said arm (17) being movable under the action of at least one pair of actuator members (23, 24) connected to the support structure (5), said arm (17) and pair of actuator members (23, 24) defining an articulated quadrilateral (15).
 23. An apparatus as claimed in claim 22, characterised in that a first one of said actuator members (23, 24) comprises a linear guide (24) fastened to the support structure (5) and having a slider (24 b) rotatably connected to a first portion (17 a) of said arm (17) to guide said first portion (17 a) along a fixed rectilinear translation direction.
 24. An apparatus as claimed in claim 23, characterised in that said slider (24 b) is connected to said arm (17) by a universal joint.
 25. An apparatus as claimed in claim 24, characterised in that said linear guide (24) comprises a screw threaded rod (24 a) on which a threaded portion of said slider (24 b) is rotatably engaged, rotation of said threaded rod (24 a) generating translation of said slider (24 b) along a major extension direction of the threaded rod (24 a).
 26. An apparatus as claimed in claim 25, characterised in that the second one of said actuator members (23, 24) is a linear actuator (23) acting between a second portion (17 b) of said arm (17) and the support structure (5) to rotate the arm (17) around a hinging fulcrum (22) relative to the first actuator member (24).
 27. An apparatus as claimed in claim 26, characterised in that said linear actuator (23) has a first end secured to said support structure (5) by a fixed-axis hinge (C) and a second end hinged on said second portion (17 b) of said arm (17).
 28. An apparatus as claimed in claim 17, characterised in that in said first operating position, the linear actuator (23) is disposed along said first common plane (Y1).
 29. An apparatus as claimed in claim 17, characterised in that said guide means comprises one said articulated kinematic mechanism (13) for each of said first (2) and second (3) rollers.
 30. An apparatus as claimed in claim 17, characterised in that said at least one articulated kinematic mechanism (13) comprises two articulated quadrilaterals (15) acting on axially opposite ends (Z) of a respective roller (2, 3) and operable independently of each other to enable calendering of plates (L) according to conical conformations.
 31. An apparatus as claimed in claim 17, characterised in that it comprises a control box operatively interlocked with the actuator members (23, 24) of said articulated quadrilaterals (15) to move at least one of said rollers (2, 3) between a first position at which said roller (2, 3) generates a thrust towards the pressure roller (4) to give rise to a grip action on the plate (L), and a second position at which said roller (2, 3) is moved apart from the pressure roller (4).
 32. An apparatus as claimed in claim 17, characterised in that said linear actuator (23) associated with the first roller (2) is disposed at an intermediate position included between the respective linear guide (24) and the second roller (3). 